In order to find and produce hydrocarbons e.g. petroleum oil or gas hydrocarbons such as paraffins, naphthenes, aromatics and asphaltics or gases such as methane, a well may be drilled in rock (or other) formations in the Earth.
After the well bore has been drilled in the earth formation, a well tubular may be introduced into the well. The well tubular covering the producing or injecting part of the earth formation is called the production liner. Tubulars used to ensure pressure and fluid integrity of the total well are called casing. Tubulars which bring the fluid in or from the earth formation are called tubing. The outside diameter of the liner is smaller than the inside diameter of the well bore covering the producing or injecting section of the well, providing thereby an annular space, or annulus, between the liner and the well bore, which consists of the earth formation. This annular space can be filled with cement preventing axial flow along the casing. However if fluids need to enter or leave the well, small holes will be made penetrating the wall of the casing and the cement in the annulus therewith allowing fluid and pressure communication between the earth formation and the well. The holes are called perforations. This design is known in the Oil and natural gas industry as a cased hole completion.
An alternative way to allow fluid access from and to the earth formation can be made, a so called open hole completion. This means that the well does not have an annulus filled with cement but still has a liner installed in the earth formation. The latter design is used to prevent the collapse of the bore hole. Yet another design is when the earth formation is deemed not to collapse with time, then the well does not have a casing covering the earth formation where fluids are produced from. When used in horizontal wells, an uncased reservoir section may be installed in the last drilled part of the well. The well designs discussed here can be applied to vertical, horizontal and or deviated well trajectories.
To produce hydrocarbons from an oil or natural gas well, a method of water-flooding may be utilized. In water-flooding, wells may be drilled in a pattern which alternates between injector and producer wells. Water is injected into the injector wells, whereby oil in the production zone is displaced into the adjacent producer wells.
A horizontal, open hole completion well can comprise a main bore or a main bore with wanted side tracks (fishbone well) or a main bore with unwanted/unknown side tracks.
Further, a horizontal, open hole completion well may, when producing hydrocarbons (producer well) or when being injected with water (injector well) be larger than the original drilled size due to wear and tear.
Additionally, horizontal, open hole completion wells can have wash outs and/or cave ins.
Thus, a need exist to characterize open hole completion wells. The characterization may comprise e.g. measurement versus depth or time, or both, of one or more physical quantities in or around a well.
In order to determine such characteristics of an open hole completion, wireline logging may be utilized. Wire-line logging may comprise a tractor which is moved down the open hole completion during which data is logged e.g. by sensors on the tractor.
However, an open hole completion may comprise soft and/or poorly consolidated formations which may pose a problem for existing tractor technologies. For example, chain tracked tractors may impact the wall of soft and/or poorly consolidated formations with too large a force, and tractors comprising gripping mechanisms may rip of pieces of the soft and/or poorly open hole completion wall. A further problem of tractors comprising gripping mechanisms is the restriction in outer diameter, due to the drilled well, of the tractor which may restrict the length and mechanical properties of the gripping mechanisms.
A further problem of the existing tractor technologies with respect to e.g. horizontal open hole completion wells is that the open hole completion may have a diameter varying from the nominal inner diameter of 8.5 inch of the cased completion hole due to e.g. wash-outs and/or cave ins.
Thus, it may be advantageous to be able to move a tractor through an open hole completion well possibly containing soft and/or poorly consolidated formations.
Therefore, an object of the invention is to enable movement of a device through an open hole completion well possibly containing soft and/or poorly consolidated formations.